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FACE with crops: data for
climate change impact models
Hans-Joachim Weigel,
Remy Manderscheid
April 2016
2
FACE WITH CROPS: DATA FOR CLIMATE CHANGE IMPACT MODELS
Thünen à la carte 4a · 2016
FACE with crops: data for
climate change impact models
Hans-Joachim Weigel, Remy Manderscheid
The rapid rise of the atmospheric CO2 concentration [CO2] is the most prominent example of climate
change. Beside its role as a “greenhouse gas” CO2 is of fundamental importance for photosynthesis of
all plants and elevated [CO2] is known to stimulate photosynthesis of most plant species. Will such an
effect enhance growth and yield of our crop plants in the course of the overall climate change? We are
running unique field experiments to help to answer this question.
Global atmospheric [CO2] is rapidly increasing and has already
approached 400 parts per million (ppm). Projected future [CO2]
are expected to reach 470 to 600 ppm by 2050 and 900 ppm by
the end of 2100. With respect to climate change impacts on crop
yields and agricultural production, plant growth and agroecosystem models are commonly used to assess the implications of future changes in temperature and precipitation along with increasing [CO2].
Most often the results of these models strongly depend on
whether or not and to what extent the “CO2-fertilization” is included into these models (Figure 1; Hertel 2015). Thus, it is of particular importance to know the magnitude of such a CO2 effect under
real field conditions.
Modeled yields
HOW DO PLANTS RESPOND TO ELEVATED ATMOSPHERIC CO2
CONCENTRATIONS?
In C3 crops like wheat, rice, sugar beet and soybean the enzyme RuBisCO is converting CO2 into an organic molecule with three carbon
atoms. However, at current ambient CO2 levels RuBisCO remains
non-saturated with respect to CO2. Consequently, elevated [CO2] enhances carbon assimilation of these crops. For example, an enhancement of the photosynthetic rate of up to 35-50 % may be possible
at a [CO2] of 550 to 750 ppm. Due to a different CO2 fixation mechanism photosynthesis of C4 crops like maize, sorghum and sugarcane
is not enhanced by elevated [CO2]. However, under elevated [CO2]
leaf stomatal conductance of both plant types is reduced resulting
in a decrease of leaf transpiration. This again may lead to a more
Plant available soil water
without CO2 effect
2011
with CO2 effect
yield change (%)
10
5
0
2020
2050
2080
2020
2050
2080
-5
-10
climate models:
ECHAM4
HadCM2
CGCM1
CSIRPO-Mk2b
GFDL-R15
Figure 1: Modeled (DSSAT-CERES) yields of winter wheat in Austria for different
climate change scenarios with and without “CO2-fertilization“ (Alexandrov et al.
2002; modified)
plant available soil water
120
100
wet
80
60
40
20
0
385 ppm
600 ppm
wet
dry
maize
sorghum
26.06.
10.07.
dry
24.07.
07.08.
21.08.
04.09.
18.09.
02.10.
Figure 2: Plant available soil water content (mm; 0-60 cm) of maize (cv. Simao)
and sorghum (cv. Bulldozer) canopies during FACE-experiments in Braunschweig under adequate (wet) and reduced (dry) water supply
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FACE WITH CROPS: DATA FOR CLIMATE CHANGE IMPACT MODELS
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Photo 1: Free air CO2 enrichment (FACE) rings in a winter wheat field during July (Braunschweig). Across the area surrounded by the vertical vent pipes (light green) the CO2
concentration is elevated to 600 ppm.
efficient plant water use. Moreover, in C3 plants elevated [CO2] leads
to changes in the plants tissue composition with consequences for
e.g., plant quality. For any climate change impact assessments it
is important to know how these primary effects of elevated [CO2]
translate into effects on crop yields and yield quality. We are addressing these questions in FACE experiments.
FACE: OPTIMAL TOOL TO STUDY THE “CO2 FERTILIZATION
EFFECT“
The FACE technology (Free Air Carbon Dioxide Enrichment) allows
to simulate future atmospheric CO2 levels under open field conditions – without any enclosure of plant canopies by chambers or
greenhouses. In Braunschweig (North Germany) we have applied
a circular FACE system in an arable crop field for now more than
10 years (Photo 1). The system is used to raise the atmospheric
[CO2] to 550 or 600 ppm during the growing season (daylight only).
In order to assess the interaction between elevated [CO2] and
drought stress we developed a rain-out shelter system that can be
combined to the FACE apparatus (Manderscheid et al. 2014; Photo 2). FACE experiments are currently considered as the optimal
tool to simulate future atmospheric CO2 scenarios for plants close
to reality, e.g. as canopy microclimate and overall in situ growth
conditions are not affected. Only a limited number of FACE experiments has been carried out as they are technically complex and
expensive to run due to high CO2 costs.
ELEVATED CO2 REDUCES PLANT WATER CONSUMPTION AND
ENHANCES YIELDS
In FACE experiments in an arable crop rotation with winter barley,
sugar beet and winter wheat (C3 plants) and with different geno-
types of maize and sorghum (C4 plants) we were able to shown
that due to a reduced leaf transpiration total canopy transpiration
also decreased. At the same time soil water content in all these
experiments increased under elevated [CO2] (Figure 2). One may
speculate that such an effect may help plants to better cope with
dry conditions which are expected to increase along with climate
change.
A great number of CO2 enrichment experiments during the last
30 years – mostly carried out under artificial, non-natural growth
conditions – revealed positive growth and yield effects of elevated [CO2] on various crop species. Growth enhancements of up
to 30 % were observed at CO2 concentrations ranging between
200 to 300 ppm above the respective ambient air levels (350-380
ppm). However, these results vary considerably across the individual experiments. In comparison, growth stimulating effects observed in FACE experiments carried out in USA, Japan, China and
Australia were mostly lower and amounted – on average – to ca.
15 % under a [CO2] of 550 ppm (Long et al. 2006).
Similar growth and yield enhancements ranging between 9 to
15 % (Table 1; Weigel and Manderscheid 2012) were observed in
our FACE experiments in Braunschweig, which are the only FACE
experiments carried out in Europe in arable crop rotations. While
it has mostly been observed that the relative growth stimulation
by elevated [CO2] is lower at low compared to adequate nitrogen supply, this could hardly been observed in our experiments
(Table 1). Also, for the first time we were able to show in a field
experiment under FACE conditions that for maize a “CO2 fertilization effect” could only be observed if the plants suffer from water
stress conditions which clearly decrease above-ground biomass
production (Table 2; Manderscheid et al. 2014).
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FACE WITH CROPS: DATA FOR CLIMATE CHANGE IMPACT MODELS
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Photo 2: Free air CO2 enrichment (FACE) system in Braunschweig combined to “rain-out shelters“ in order to simultaneously simulate drought stress conditions (coloured
area = CO2 enrichment).
In general, overall assessments of the extent of the “CO2 fertilization effect“ under real field conditions in the future remain difficult. There still is information with only a limited number of crop
species and very little is known about the possible interactions of
elevated [CO2] with other growth variables (temperature, water
and nutrient supply). Also, possible differences in the CO2 response between different genotypes of a species remain mostly unknown. Controversy also remains whether data from field or also
from laboratory experiments provide suitable information that
can be used in models for climate change impact assessments.
For example, growth chamber experiments are assumed to overestimate the positive growth effects of elevated [CO2] in comparison to FACE experiments, and thus too strongly qualify negative
effects of climate change. This is equally true for assessments of
possible effects of increasing frequencies of climate extremes
and climate variability.
ELEVATED CO2 CHANGES PLANT QUALITY
Almost all studies under elevated [CO2] revealed changes of the
concentrations of macro- and micro-elements (e.g. nitrogen
sulfur, iron, zinc) and of other organic compounds (e.g. soluble
sugars, vitamins, secondary metabolites etc.) in the plant tissue.
For example, in grains of various cereal species elevated [CO2] induced a reduction of the total nitrogen concentration which corresponds to a loss of protein. In our FACE experiments with winter
wheat we not only observed a loss of crude protein content of
10-15 % but also changes in the relative amounts of individual
protein fractions (glutenines vs. gliadines) which contribute to
the total protein content, an effect which may have consequences for the baking quality of flour (Wieser et al. 2008). Changes
of important plant constituents (e.g. protein, mineral and trace
element content) induced by elevated [CO2] are of importance as
this might exacerbate the problem of ”hidden hunger” (Myers et
al. 2014) which is particularly relevant for developing countries.
FACE-DATA FOR MODELS
Data from the FACE experiments in Braunschweig are used by
modeling groups from Germany and abroad, in order to validate, calibrate and improve different models for the assessment of
future crop yields under climate change. For example, this was
done for an analysis of climate change impacts on German wheat
production (Kersebaum and Nendel 2014). Data of our maize experiments were provided to the maize modeling team of AgMIP
(the Agricultural Model Intercomparison Projects) in order to test
if current maize crop models catch the impact of future [CO2] on
maize yield and water use. Crop modeling for climate change impact assessments came up with the prediction some years ago
that under future climate change wheat yield might be more impaired by heat stress rather than by drought conditions. However,
these models were mainly based on findings from growth chamber and greenhouse studies. Therefore, most recent FACE experiments in Braunschweig were initiated, where CO2 enrichment is
combined to simultaneous short-term heat treatments of wheat
canopies (Photo 3), in order to elucidate possible interactions of
heat stress and elevated [CO2] effects under real field conditions
and to provide new data for the related modeling approach.
IMPLICATIONS FOR PLANT BREEDING
FACE and open-top chamber experiments in Braunschweig have
shown that (i) some of our current crop species are unable to fully
exploit the positive growth effects of elevated [CO2] and (ii) that
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FACE WITH CROPS: DATA FOR CLIMATE CHANGE IMPACT MODELS
Thünen à la carte 4a · 2016
Photo 3: Free air CO2 enrichment
(FACE) combined to heat stress
treatments of winter wheat during
anthesis (Braunschweig). Inside the
FACE area surrounded by the black
vertical vent pipes the CO2 concentration is elevated to 600 ppm. H-1
and H-2 = plots with temperature
treatments applied by six infrared
heaters. Con = control treatment
with dummy heaters.
Crop
Nitrogen
supply
Parameter
CO2-effect
(%)
Barley
100
50
Grain yield
+ 12.0
+ 13.1
Ryegrass
100
50
Above-ground
biomass
+ 8.8
+ 9.8
Sugar beet
100
50
Sugar yield
+ 10.3
+ 14.2
Wheat
100
50
Grain yield
+ 15.6
+ 11.7
Table 1: Effects of FACE (550 ppm) and different nitrogen (N) fertilization levels
on yield parameters of different crop species in a crop rotation in Braunschweig
(100 = adequate fertilization; 50 = 50 % of adequate). Results are shown as
percent change compared to ambient air [CO2].
1st growing season 2nd growing season Drouht stress
wet
dry
wet
dry
effect (2nd season)
385
ppm
10.4
10.0
11.3
7.3
- 39.5 %
550
ppm
10.3
10.2
11.2
10.2
- 14.5 %
CO2effect
-1 %
1 %
-1 %
41 %
Table 2: Effects of FACE on grain yield (t/ha) of maize in Braunschweig under
adequate (wet) and reduced (dry) water supply and relative CO2- and drought
effects. During the 1st growing season drought stress could not be induced.
different genotypes of a particular species differ in their response
to more CO2. This raises the question, whether and to what extent
there might be possibilities for more targeted breeding strategies
to “optimize” the “CO2 fertilization effect” in order to maximize
the benefits from the high atmospheric CO2 supply. Further FACE
experiments are required to screen large numbers of genotypes
of a particular crop species (e.g. winter wheat) for their relative
growth responses to elevated [CO2].
Long, S. P., E.A. Ainsworth, A.D.B. Leakey, J. Nösberger and
D.R.Ort: Food for thought: Lower-than expected crop yield stimulation with rising CO2 concentrations. Science 312 (2006), S.
1918-1921
REFERENCES
Myers, S.S., A. Zanobetti, I. Kloog, P.Huybers, A.D. Leakey, A.J.
Bloom et al.: Increasing CO2 threatens human nutrition. Nature
510 (2014), S. 139-142
Alexandrov, V., Eitzinger, J., Cajic, V., and M. Oberforster: Potential impact of climate change on selected agricultural crops in
north-eastern Austria. Global Change Biology 8 (2002), S. 372-389
Manderscheid, R., M. Erbs and H.J.Weigel: Interactive effects of
free-air CO2 enrichment and drought stress on maize growth. European Journal of Agronomy 52 (2014), S. 11-21
Hertel T.W.: The challenge of sustainably feeding a growing planet.
Food Security 7 (2015), S. 185-198
Weigel, H.J. and R. Manderscheid: Crop growth responses to free
air CO2 enrichment and nitrogen fertilization: Rotating barley,
ryegrass, sugar beet and wheat. European Journal of Agronomy
43 (2012), S. 97-107
Kersebaum, K. and C. Nendel: Site-specific impacts of climate
change on wheat production across regions of Germany using
different CO2-response functions. European Journal of Agronomy
52 (2014), S. 22-32
Wieser, H., R. Manderscheid, M. Erbs and H.J. Weigel: Effects of
elevated atmospheric CO2 concentrations on the quantitative
protein composition of wheat grain. Journal of Agricultural Food
Chemistry 56 (2008), S.6531-6535
Zitationsvorschlag – Suggested citation:
Weigel H-J, Manderscheid R (2016)
FACE with crops: data for climate
change impact models. Braunschweig:
Johann Heinrich von Thünen-Institut,
6 p, Thünen à la carte 4a,
DOI:10.3220/CA1455111790000
Thünen à la carte 4a
April 2016
Herausgeber/Redaktionsanschrift
Thünen-Institut
Bundesallee 50
38116 Braunschweig
Germany
[email protected]
www.thuenen.de
ISSN 2363-8052
DOI:10.3220/CA1455111790000
Fotos: Thünen-Institut